The present invention generally relates to a light sensor system and to a method for detecting ambient light and more particularly, to an ambient light sensor system which accurately detects the level of ambient light in a logarithmic manner, which allows a cost effective analog to digital converter to be used in combination with a single positive voltage or energy type power supply, and which reduces and/or substantially minimizes dark current and temperature related errors.
A light sensor is used to detect the level of ambient light (i.e., the amount or xe2x80x9clevelxe2x80x9d of light present or occurring within the environment that the sensor is disposed within) and to produce an output signal representative of the detected amount or level of such ambient light. The produced output signal is then used by a wide variety of devices and assemblies, such as display devices, to operationally adjust one or more respective attributes or characteristics (e.g., the intensity of a displayed image) of these devices and/or assemblies.
While light sensors do generally detect the level of such ambient light, they suffer from some drawbacks. For example and without limitation, the measurement accuracy of a linear light sensor system remains substantially constant over its operational range and does not desirably provide increased accuracy and resolution as the light level decreases. Moreover, the measurement accuracy of silicon type photodiode sensors at relatively low illumination levels are often undesirably reduced by xe2x80x9cdark currentxe2x80x9d error which is generally a function of temperature and reverse bias voltage.
While some attempts have been made to produce a light sensor system and a concomitant method to detect ambient light which overcomes these previously delineated drawbacks, such attempts require a relatively costly and relatively highly accurate analog to digital converter and/or a relatively costly and complicated digital signal processing assembly, and may further require a relatively costly and complicated power assembly which is operative in both the positive and negative electrical power ranges.
There is therefore a need for a new and improved light sensor system and a method for detecting ambient light which overcomes some or all of the previously delineated drawbacks associated with prior light sensors and prior methods for detecting ambient light.
It is a first object of the present invention to provide a light sensor system and a method for detecting ambient light which overcomes some or all of the previously delineated drawbacks of prior light sensor systems and prior methods for detecting ambient light.
It is a second object of the present invention to provide a light sensor system and a method for detecting ambient light which overcomes some or all of the previously delineated drawbacks of prior light sensor systems and prior methods for detecting ambient light by logarithmically amplifying a dynamically adjusted electrical current value.
It is a third object of the present invention to provide a light sensor system and a method for detecting ambient light which overcomes some or all of the previously delineated drawbacks of prior light sensor systems and prior methods for detecting ambient light by the use of a single electrical power supply assembly which operatively provides electrical power only in the positive power range.
It is a fourth object of the present invention to provide a light sensor system and a method for detecting ambient light which overcomes some or all of the previously delineated drawbacks of prior light sensor systems and prior methods for detecting ambient light by providing a light sensor system output voltage range which is compatible with a rather limited analog to digital converter input voltage range and, more particularly, varies from about zero volts to about five volts.
It is a fifth object of the present invention to provide a light sensor system and a method for detecting ambient light which overcomes some or all of the previously delineated drawbacks of prior light sensor systems and prior methods for detecting ambient light and which produces a relatively accurate output signal which is resistant to temperature variation and dark current type errors.
It is a sixth object of the present invention to provide a substantially omnidirectional light sensing system and method which is resistant to shadowing effects in a diffuse ambient lighting environment and which is adapted to detect the illumination level of direct specular sunlight from substantially all semi-hemispherical angles.
According to a first aspect of the present invention, a light sensor system is provided. The light sensor system produces an electrical current signal which is representative of an amount of light, which creates a current reference and a voltage offset signal, and which further logarithmically amplifies the ratio of the produced current signal and the reference current signal and adds the amplified ratio to the voltage offset signal, thereby creating a light detection signal.
According to a second aspect of the present invention, a method for detecting ambient light is provided. The method includes the steps of producing a first signal by the use of the ambient light; producing a second signal; and logarithmically amplifying the first and the second signal, thereby producing an output signal which is indicative of the amount of ambient light.
These and other features, aspects, and advantages of the present invention will become apparent from a reading of the following detailed description of the preferred embodiment of the invention and by reference to the following drawings.